The coolant circulation is thermostatically controlled. As long as the engine is cold, the coolant circulates only in the cylinder block, and the thermostat in the coolant system heat exchanger opens and forces a flow of coolant through the radiator. The coolant is driven by a coolant pump, which is driven by a V-belt in the 4-cylinder petrol engine and by a toothed belt from the camshaft in the diesel engine. The coolant passes through an aluminum radiator and is cooled by the air flow blown over the radiator fins. In cars with an automatic transmission, a radiator is used to cool the gearbox oil, located in the left radiator tank.
At high coolant temperatures, an electric fan provides additional cooling of the coolant. As soon as the coolant temperature exceeds 100°C, the electric fan turns on; in a diesel engine this is done via a thermal switch, in petrol engines the engine control unit switches on the fan via a relay. As soon as the coolant temperature drops, the fan switches off.
The expansion tank serves as a container for the coolant, collects the coolant that expands under the influence of heat and, after cooling, feeds it back into the circuit. As a result, this circuit is constantly filled and ensures good cooling. Coolant can only be added through the expansion tank.
Warning! The electric fan may spontaneously turn on repeatedly when the engine is off, if the ignition is on. This is caused by heat accumulated in the engine compartment. Therefore, if possible, turn off the ignition when performing work in the engine compartment.
Coolant circuit: 1 - Heating system heat exchanger; 2 - Engine; 3 - Thermostat housing; 4 - Coolant pump; 5 - Coolant expansion tank; 6 - Threaded cap; 7 - Radiator; 8 - Bypass hose; 9 - Oil radiator